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Calling all ball-eyepiece aficionados!

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#1 smallscopefanLeo

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Posted 31 October 2012 - 05:16 PM

Gentlemen, should I take the plunge? I am currently contemplating the purchase of one of Mr. Siebert's mystique-enshrouded Ball Planesphere eyepieces here (I am specifically eyeballing the Fused Silica 6.5 or perhaps the the BK7 7.5)

I have scoured the archives, which yielded the one main long thread about the introduction of these (which is scant on much real world information, but heavy on the ocular innuendo http://www.cloudynig...at.php/Numbe... :bigblush:) and a half dozen other brief allusions, which tantalize me with their hintings of unrivaled on-axis planetary light reflection corralin' powers). I do understand, based on my readings, that we are talking some of the paltriest eye relief, fields of view, and off-axis image integrities around, but it is that sweet spot that beckons! I have a small driven mount to help me make use of one of these should Santa deem me to have been a good boy this year. :jump:

I would like to hear from those who have been using these at any time over the course of the past couple of years. Should I go for it? I've got an itch here (and focal length void in-between the 6-8mm range, yikes) that's positively begging to be scratched! :scratchhead: Thanks in advance! :thanx:

#2 MRNUTTY

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Posted 31 October 2012 - 09:00 PM

While I don't have any of his ball EP's, the MonoCentric's I do have sport great on axis performance. The Barlows are super too. I have some small FL SS's on order too. I would say; if that's what you want, go for it.

#3 Sarkikos

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Posted 01 November 2012 - 09:40 AM

Don't do it! You'll put your eye out!

But seriously... I made a 5.8mm ball eyepiece a couple years ago. The usable AFOV was only about 10 degrees, and I'm being generous. My best scopes do not track. It was an exercise in stupidity ... I mean futility to try to keep a planet in that vanishingly small though sharp FOV. Well, I assume it was sharp, because I couldn't look at the planet long enough to get a good view.

The bottom line: If your prime planet scopes don't track, don't get a ball eyepiece. But since you say you have tracking, maybe you should give a ball eyepiece a try. Just be sure that thing tracks very accurately!

Mike

#4 Jim Rosenstock

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Posted 01 November 2012 - 10:41 AM

I agree with Mike. Tracking is absolutely essential.

Absolutely on-axis, they are as good as anything. I was especially taken with their performance on Jupiter; Saturn and Mars, not so much.....the Moon, fuggedaboutit!

FWIW, I feel that the BK7 balls have a slightly bigger "sweet spot" than the Fused Silica, but still very tight in the center....

Worth a try?? Yup.

Jim

#5 BillP

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Posted 01 November 2012 - 11:52 AM

Are you a planetary observer? Are you fanatical about your planetary observing? Is Mars your favorite planet?

If you answered yes to most of those, then worth getting one IMO. Yes, only about the central 10 degrees of the AFOV is sharp. The rest is aberrated to high heaven and only usable to locate the target for centering. So that must be the expectation that you come to terms with. However, the on-axis is sublime and shows more contrast than any other eyepiece IME...including ZAOs. It's an easy tell for my eye. Of all the planets this extra contrast boost seems to have the most advantage on Mars I would say. Polar caps pop resoundingly bright white. Subtle surface features that are not detectable in other eyepieces now show, and the extent of feature that are visible increase.

I would also call Harry on these. I am not understanding why his website says that special attention is given for the Fused Silica ones and not mention of same with the BK7. So ask him why...plus ask him if either are coated and if coated how (fully, multi?). Finally ask him if the surface precision is at the same level on both or if one is made to a higher tolerance.

I'm not sure if the hemisphere of the ball on his protrudes above the housing top. If so (I made mine this way, as did SteveC), then the ER actually feels very comfortable FYI.

#6 Sarkikos

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Posted 01 November 2012 - 01:50 PM

Ahh... the orographic clouds of Mars!

#7 BillP

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Posted 01 November 2012 - 03:36 PM

Ahh... the orographic clouds of Mars!


Yes...that certainly was exciting for me. However, more than just that too :) Many of the common features show extention not visible at all in the other eyepieces as well, which is always a treat. Limb haze is also much more prominent and extended. Mars is by far my favorite planet as it can be small and quite a challenge, and can't imagine not having a ball lens for it :grin:

#8 smallscopefanLeo

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Posted 01 November 2012 - 06:30 PM

Hello John, Mike, Jim and Bill, thank you all :thanx: very much for sharing your experiences and insights here in regards to this intriguing eyepiece design. I am a relative newbie that has been lurking on Cloudy Nights off and on over the course of the past three years or so, and that has been gradually collecting a small ménagère of affordable grab and go scopes. My main interests so far are indeed in the realms of Solar, Lunar and Planetary observations.

John, I wish you hadn't mentioned those MonoCentrics and the barlows, as both are high up on my list of 'most desireable items to acquire.' I am trying hard to exercise restraint and to not blow the budget! I am glad to hear that your experiences with both of those have been great so far, thanks for sharing. It is very tempting to collect more of a series, or a specific make, after a successful purchase has been made. That is partly why I am hedging here, as knowing myself, I will not easily be able to stop at just the purchase of one item from those different lineups of eyepieces and barlows :help:, if I end up being satisfied with the first one I choose here.

Mike, I have a NexStar SLT type mount (mine is technically the GT model that Costco has been selling with their Celestron scopes over the past year or so, and that I purchased as the mount alone from an Astromarter earlier this year). Ok, point taken about the vanishingly small FOV, thanks! ... If I do jump in here with this (which I am becoming quite convinced to), then I will brace myself for the worst! :tonofbricks:

Jim, good to know that about the BK7, thanks. If I am remembering right here, then it was mainly your posts from over the past year or two, that I found in old threads and read recently while searching for anything that I could dig up about these 'odd ball' eyepieces, and which actually mentioned time spent observing with them :waytogo:. Such glowing reports of the on-axis images of the planets through these are partly what's been luring me towards them. These responses from you guys here are pretty much sealing the deal for me ...

Bill, thank you for the advice, I will definitely call Harry before I buy. I do yearn to get better views of Mars, without a doubt. While I have had some decent observations of Mars earlier this year, and last, I have not yet had any to really write home about (which has been almost entirely the fault of my own, but also seeing and equipment related, yeah, that's it!). I was intimidated for the longest time, but have just recently gotten to really correctly collimating my little newt, which is a Synta made 'Skywatcher' 5.1" F/5 650mm. I don't think that it was badly collimated at all before, based on my meager experience as I was still getting great all-around views, but it did apparently need that extra little tweak to get it into the perfect 'zone' in which I could up the magnification much past 200x (and up to around 250x when nights were still, and even around 275x or so during some incredible moments of stillness! :drool5:) and now the views through it are even more breathtaking when the seeing is excellent (thanks in part to my new Astrosystems 1.25" Lightpipe and 1.25" Autocollimator).

Luna is still my number one object to view though, I confess! :cool: I never get tired of her geography ... I am hoping to actually use this ball eyepiece to really narrow in with that tunnel-like view and thus pick up on specific details in the terrain that way, to help me focus. (Proud new owner of Rukl's old Moon Mars and Venus here!) I am also hoping that the keypad arrows on the SLT mount will be fine enough to work with such a narrow FOV when using this eyepiece for scanning the lunar surface. Jupiter and Saturn have been my next two favorite destinations to head for, and I am beginning to observe our Sun more regularly now as well, with a Baader white light astro solar film filter and making it a point to get out there with my main achro refractor (which is also made by Synta, a Skywatcher 80mm F/11.25) for at least a brief session here and there to keep tabs on her activity. My next purchase scope-wise is actually planned out to be the Costco special Celestron 102GT F/10 that so many here are raving about, and which uses the same mount I now have, so I will have a back-up goto mount (I also have an AZ4 for freestyle viewing), and more importantly a 1000mm F/10 to use when aiming for Mars next season! :jump:
Edit: For the record I am very fortunate to have a small assortment of drool-worthy-to-me eyepieces currently, including all of the RKE's (and the barlow!), the 12.5, 18 and 25 Volcanoes, and an odd assortment of Plossls and barlows (barlows are addicting). I am sure that this won't substitute for any of those, and most likely I will still be tempted to get a 7mm ortho as well eventually, and maybe also a 9mm too :whistle:, but I just can't resist the idea of this design here ... it just seems like simplicity in itself. While I don't usually follow the tenet of 'less is more' personally (I wish I could), I am in awe of most people and things that do.)

Thank you all again! :salute:
Leo

#9 tomharri

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Posted 01 November 2012 - 07:57 PM

I don't know,
But I've been told,
To send all my money to Televue,
And Pentax,
There is way more Satisfaction,
Down that road.

#10 MRNUTTY

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Posted 02 November 2012 - 06:50 AM

John, I wish you hadn't mentioned those MonoCentrics and the barlows, as both are high up on my list of 'most desireable items to acquire.' I am trying hard to exercise restraint and to not blow the budget! I am glad to hear that your experiences with both of those have been great so far, thanks for sharing. It is very tempting to collect more of a series, or a specific make, after a successful purchase has been made. That is partly why I am hedging here, as knowing myself, I will not easily be able to stop at just the purchase of one item from those different lineups of eyepieces and barlows :help:, if I end up being satisfied with the first one I choose here.


Yeah, I have the same disability; when I buy something I like, I get the rest too :-)

Also, I like to support the small businessman. Not that these are a charity buy! I really like these mono's. With all the hoopla around vintage mono's, I'm glad I can find some modern ones that look to me, as good as the as the ones I can only hear about. You might want to check out Russell optics too, he builds his own EP's from Japanese stock glass. He also creates some nice EP's with a classic design; the Konig. It's nice to find a vendor that produces something beyond the ubiquitous wide-field, ortho, and Plossl.

#11 Jim Romanski

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Posted 02 November 2012 - 08:53 AM

Hey Leo

I too did some experimenting with a Ball eyepiece. I bought it from a CN member who made it and then I tried a couple of different balls in it. It was a fun project if for no other reason then being able to actually make/modify an eyepiece myself and for so little money.

I did not like using it for the Moon. The field curvature is exteme and mine have no field stop so finding the center is tricky. It really gives you a fun house experience on the lunar surface for everything outside about 20-30 degrees in the center.

We discovered that the Lanthanum balls had a ghosting problem. Harry stoppind selling these about a week after we started reporting this.

I haven't tried BK7 yet but the Fused Silica work well. Personally I find they have too much scattered light probably due to the lack of anti-reflection coating. The Pentax XO has such a deep dark field around planets it really shows the importance of controlling stray light.

But the Ball eyepieces cost a lot less than the Pentax so it's certainly not an expensive experiment.

#12 tomharri

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Posted 02 November 2012 - 01:48 PM

Here are my ball lens results from 6 months ago.
Test objects Mars and Saturn.
Test scope APM 107/700, about 250x with these.
Edmund 4mm balls fit in 4mm ortho housing and all about 3mmf.l.
Comparison lens Pentax XO 2.5mm

Ruby- too dark, a double image like misaligned binocs.
Saffire- worse than ruby.
N-LasF9- almost as good as Pentax.
BK-7- about same as laser ball.
Fused Silica- Best, same as Pentax.

There is a formula in Edmund catalog and website to calculate focal length of the various ball sizes with index of refractions. It was an interesting experiment, just handle the pieces on a tray with raised sides because you will drop something and the soft plastic tweezers hold the lenses better than metal or bamboo. Otherwise ZZIIINNNGGG... where did that lense go?

#13 Jim Romanski

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Posted 03 November 2012 - 09:47 AM

It was an interesting experiment, just handle the pieces on a tray with raised sides because you will drop something and the soft plastic tweezers hold the lenses better than metal or bamboo. Otherwise ZZIIINNNGGG... where did that lense go?

I say you've never really lived on the edge till you've coated your ball lenses with sesame oil and tried to pick them up with chopsticks. :roflmao:

#14 Sarkikos

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Posted 03 November 2012 - 10:56 AM

Comparison lens Pentax XO 2.5mm

Ruby- too dark, a double image like misaligned binocs.
Saffire- worse than ruby.
N-LasF9- almost as good as Pentax.
BK-7- about same as laser ball.
Fused Silica- Best, same as Pentax.


Yes! Now that I have an XO 2.5 and a 5.1, why bother with ball eyepieces? The ball eyepieces are no sharper than the XO's, while the XO's have - in comparison - a huge usable FOV and luxuriously comfortable eye relief.

Maybe it's time for me to sell my 5.8mm BK-7 Ball Eyepiece? It's almost as good as an XO!

:grin:
Mike

#15 BillP

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Posted 03 November 2012 - 11:54 AM

Personally I find they have too much scattered light probably due to the lack of anti-reflection coating.


I would say this is probably due to a less than well polished surface. In a recent study on scatter in optics, it was revealed that coating technology can not reduce the scatter induced by the polish on the substrate of the glass (i.e., light ray being reflected in multiple random directions). In fact, it increases it depending on the precision of the application of the coatings. Multicoatings being more difficult to add scatter since there are multiple coatings each having to be perfectly applied and particulate/bubble free.

Since a spherical lens is of course strongly curved, and since it is a singlet, there is no issue with ghosting or reflected light bouncing between elements or anyplace that can cause ghosting, further reducing contrast due to this, in addition to the contrast loss from scatter. So in a well polished uncoated ball lens, you should just have a 2 surface uncoated light transmission loss (92% efficiency) and very very little visible scatter or halo around bright objects. The "tech-spec" spheres I have produce almost zero scatter around planets and stars compared to any of my normal production eyepieces.

#16 Jim Romanski

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Posted 08 November 2012 - 05:35 PM

I would say this is probably due to a less than well polished surface.


You know Bill I’m not sure that it’s from the polish or what it’s from. I believe I’m using the same "tech-spec" spheres from Edmunds that you are.

All I know is that the Ball eyepieces seem to have sharp focus at their very narrow sweet spot. But I find the contrast of to be a bit washed out.

Since a spherical lens is of course strongly curved, and since it is a singlet, there is no issue with ghosting or reflected light bouncing between elements or anyplace that can cause ghosting, further reducing contrast due to this, in addition to the contrast loss from scatter.


Well I wouldn’t say there isn’t any place that can cause ghosting. Remember, at least a couple of us saw ghosting with the lanthanum balls that made them unusable. The housing of the eyepiece even if it is well blackened can still reflect light. And what about within the ball itself?

I can speculate on why I see what I see but in the end unless I were to try to systematically eliminate the cause I’m only guessing.

#17 Jeff B

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Posted 08 November 2012 - 07:00 PM

I would say this is probably due to a less than well polished surface.


You know Bill I’m not sure that it’s from the polish or what it’s from. I believe I’m using the same "tech-spec" spheres from Edmunds that you are.

All I know is that the Ball eyepieces seem to have sharp focus at their very narrow sweet spot. But I find the contrast of to be a bit washed out.

Since a spherical lens is of course strongly curved, and since it is a singlet, there is no issue with ghosting or reflected light bouncing between elements or anyplace that can cause ghosting, further reducing contrast due to this, in addition to the contrast loss from scatter.


Well I wouldn’t say there isn’t any place that can cause ghosting. Remember, at least a couple of us saw ghosting with the lanthanum balls that made them unusable. The housing of the eyepiece even if it is well blackened can still reflect light. And what about within the ball itself?

I can speculate on why I see what I see but in the end unless I were to try to systematically eliminate the cause I’m only guessing.


To help with contrast, make sure you blacken the edges. :grin:

#18 Alan A.

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Posted 10 November 2012 - 08:59 PM

Alright, you guys got me going. I ordered the FS 6.5 from Harry.

He indicates there is no difference in the view between the bk7 and the fused silica. Both are made to the same tolerances, and neither has any coatings.

I asked him if these eyepieces would work in my 24 3.3, he indicated they would work well, which i was a little surprised to hear.

I'm looking forward to testing this eyepiece on jupiter.






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